Pyroelectric device

ABSTRACT

A pyroelectric device is arranged such that a pyroelectric member sensitive to infrared rays is incorporated in a casing composed of a can and a stem made of materials with similar thermal expansion coefficients. A filter for sealing a window hole for introducing infrared rays into the inside of the pyroelectric device is fixed to the window hole by a fusing agent of silver solder. Electrodes are formed on the upper and lower surfaces of the pyroelectric member and are composed of an absorbing electrode portion for absorbing infrared rays and a drawing electrode portion for outputting an electric signal by sensing the infrared rays. The absorbing electrode portion is composed of an infrared ray absorbing material formed in a thin layer. The drawing electrode portion is composed of the same material formed in a layer thicker than that of the absorbing electrode portion. Terminal pins passing through the pyroelectric device for outputting the electric signal are provided with flat collars near the extreme ends of the terminal pins. A printed board for internally processing the electric signals is abutted against the flat collars so that it is stably supported on the terminal pins in parallel with the filter.

BACKGROUND OF THE INVENTION

The present invention relates to a pyroelectric device used as aninfrared-ray sensor and heat sensitive device.

A pyroelectric device can be used as an infrared-ray sensor using apyroelectric element composed of a material such as, for example, PVDF(polyvinylidene fluoride), PZT (lead zirconate titanate) or the like, orcan be used as a sensing device such as a flame sensor disposed in atunnel or the like to detect infrared rays of flame when fire is caused,or can be used as an intrusion detector used in a security system fordetecting infrared rays from a human body.

Conventionally, as shown in FIG. 6, a pyroelectric device is arrangedsuch that a pyroelectric member 40 and a printed board 41 are disposedon a base comprising stem 42 composed of metal or the like, and aresealed by a frame member comprising a can 43 composed of a steel plateor the like covering the upper periphery of the stem 42. The printedboard 41 includes circuit elements 61 such as a field effect transistor(FET) or the like mounted thereon to output the intensity of infraredrays detected by the pyroelectric member 40 in the form of an electricsignal. More specifically, the can 43 is provided with a lighttransmitting window hole 44 through the ceiling thereof so thatunillustrated infrared rays emitted from the flame of, for example, afire or the like are irradiated to the pyroelectric member 40 throughthe window hole 44. A filter 45 composed of, for example, silicon whichis excellent in infrared ray transmittance is disposed over the windowhole 44 to seal the same and enable the infrared rays to be transmittedtherethrough. The sealing by and the bonding of the filter 45 isperformed by forming an adhesive-bonding portion 46 with an adhesivesuch as an epoxy resin or the like.

Although the casing of the pyroelectric device is composed of the can 43and stem 42 as described above, the sealed type pyroelectric device isformed in such a manner that the can 43 and stem 42 are fused oradhesive-bonded to each other at the sealing portion 47 along theperiphery of the stem. As shown in FIG. 6, three lead terminals, thatis, a ground terminal. 48, a source terminal 49 and a drain terminal 50extend from the stem 42 and the aforesaid electric signal is output toan unillustrated main electric circuit through these lead terminals. Inthis case, although the ground terminal 48 is directly connected to thestem 42, the two other terminals, that is, the source terminal 49 anddrain terminal 50 are fixed to the stem 42 in a sealed state throughinsulating members 51 so as to be insulated from the stem 42.

Arrangement of the pyroelectric member 40 will be described in detailwith reference to the enlarged cross sectional view shown in FIG. 7. Thepyroelectric member 40 is disposed on the printed board 41 through abase member 58, and keyhole-shaped electrodes 52 and 53 each composed ofa protecting rectangular portion and a disc-shaped portion are formedrespectively on the upper and lower surfaces of the pyroelectric member40 by vapor deposition or the like. The disc-shaped portions 54 and 55of these electrodes are disposed to confront to each other across thepyroelectric member 40, and the projecting portions 56 and 57 thereofare disposed so as to extend from the disc-shaped portions 54 and 55 tothe right and left sides of the pyroelectric member 40, respectively.The electrodes 52 and 53 are composed of an infrared ray absorbingmaterial such as nickel chromium alloy, gold black or the like.

The pyroelectric member 40, base member 58 and printed board 41 arebonded and fixed to each other through a suitable material,respectively, and electrically conductive adhesives 59 and 60 areapplied between the electrodes 52 and 53 on the upper and lower surfacesof the pyroelectric member 40 and unillustrated circuit patterns of theprinted board 41 so that electric conductivity is establishedtherebetween. An electrically conductive adhesive mixed with silverfiller or the like is used as the electrically conductive adhesives 59and 60.

When the aforesaid pyroelectric device is used as, for example, a flamesensor, it is required to operate normally as well as safely andsecurely in environments having a wide range of humidities, havingcorrosive gases and having a wide range of temperatures. This is becausepyroelectric devices are used in severe environmental conditions in theindoors and outdoors such as, for example, in a factory, parking area,hot-spring resort, tunnel or the like. When an accelerated operationtest is executed in correction with the conventional pyroelectric devicearranged as described above to confirm its operation to satisfy theabove requirements, since the can 43 is composed of a steel plate andthe filter is composed of silicon, a problem arises in that the surfaceof the can 43 rusts and further the occurrence of the rust is naturallyaccelerated under the existence of the corrosive gases. In addition, agap is formed in the adhesive-bonding portion 46 adjacent to the windowhole 44 and the filter 45 cracks due, to the difference in thermalexpansion coefficients thereof.

Further, the pyroelectric device includes the filter 45 fixed over thewindow hole 44 of the can 43 by the resin adhesive-bonding portion 46.Since the bonding portion 46 is composed of the resin, a gap is liableto be formed due to the ventilating property and deterioration of theresin, although this is dependent on the characteristics of the resin,and thus the functional life of the bonding portion 46 in providing anairtight seal is very short. That is, a problem arises in that moisturecontained in the outside air or corrosive gases penetrates through thebonding portion 46 and corrodes the pyroelectric member 40 and circuitelements 61 to lower the reliability of the pyroelectric device.

Further, in this type of pyroelectric device, the electrodes 52 and 53formed on the surfaces of the pyroelectric member 40 have a function ofelectrically connecting to the pyroelectric member 40 as well as theanother function of containing infrared rays incident on thepyroelectric member 40. More Specifically, it is ideal that theelectrode 52, as a light receiving surface, absorbs the infrared rayswithout reflecting the same and the electrode 53 on the backside thereofreflects the infrared rays without causing the same to be transmittedtherethrough so as to improve the infrared racy absorbing efficiency tothe pyroelectric member 40. Therefore, the electrodes 52 and 53 areindividually formed to a predetermined optimum thickness.

The electrically conductive adhesives 59 and 60 are applied to theelectrodes 52 and 53, respectively, and when the adhesives are cured, atension is applied to the electrodes 52 and 53. Since the electrodes 52and 53 are formed thin for the purpose of absorbing infrared rays, andthus when the thin and slender electrodes 52 and 53 are subjected tocorrosion, vibration or the like, they may be easily cut off at theboundary between them and the adhesives 59 and 60. In particular, whenthe pyroelectric device is used as a flame sensor for detecting infraredrays, severe regulations regarding durability are applicable to thepyroelectric device, and it may be installed at a place with very badenvironmental conditions under which the pyroelectric device is damaged.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to electrically connectelectrodes to circuit patterns of a printed board securely withoutreducing the infrared ray absorbing efficiency of a pyroelectricelement.

Another object of the present invention is to provide a pyroelectricdevice capable of maintaining a sufficient airtightness and having acasing that maintains a weather resistance, even if the environmentalconditions such as temperature and the like change severely, withoutdamaging a filter mounted to a window portion of the casing.

A further object of the present invention is to improve an airtightnesswhen a window hole of a can is sealed with a filter and also to increasethe strength thereof.

A still further object of the present invention is to improve theparallel orientation of a printed board to a stem when the printed boardis mounted on the stem, so as to provide a pyroelectric device which hasexcellent mechanical properties and performance and also is easy to workwith.

To achieve these objects, according to the present invention, there isprovided a pyroelectric device, which comprises a stem having apyroelectric member including electrodes formed on the upper and lowersurfaces thereof for detecting infrared rays and a printed board mountedthereon, the printed board having an electric circuit for outputting theinfrared rays detected by the pyroelectric member as an electric signal,a can having a window hole and fixed to the stem in an airtight state,and a filter for sealing the window hole. Each of the electrodes formedon the upper and lower surfaces of the pyroelectric member includes anabsorbing electrode portion for absorbing infrared rays and a outputtingelectrode portion for drawing an electric signal to an electricallyconductive adhesive, the absorbing electrode portion being composed ofan infrared ray absorbing material formed as a thin layer, the drawingelectrode portion being composed of the same material formed as a layerthicker than that of the absorbing electrode portion or composed of acorrosion resistive material.

The can having the window hole for the filter and the stem whichcooperatively form a casing are composed of an alloy having theconstitution of Fe; 55%, Ni: 28% and Co: 17%. When the window hole issealed by the filter, the filter is abutted against the circumference ofthe window hole through a fusing agent and the fusing agent is meltedand then solidified to fix the filter to the window hole so that theinside of the pyroelectric device is placed in a sealed state. Terminalpins stand on the stem in communication with the outside and inside ofthe pyroelectric device to support the printed board and take output theelectric signal from the electric circuit of the printed board. Theterminal pins have collars radially projecting at the extreme endsthereof on the inner side of the pyroelectric device, whereby When theextreme ends are inserted into the pin holes formed in the printedboard, the collars are abutted against the printed board to support thesame parallel to the stem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view showing an embodiment of apyroelectric device according to the present invention;

FIG. 2 is a plan view showing a main internal portion of FIG. 1;

FIG. 3 is a schematic longitudinal cross sectional view of FIG. 2;

FIG. 4 is a longitudinal cross sectional view showing another embodimentin the same way as FIG. 3;

FIG. 5 is a longitudinal cross sectional view showing a furtherembodiment in the same way as FIG. 3;

FIG. 6 is a longitudinal cross sectional view showing a conventionalpyroelectric device; and

FIG. 7 is a longitudinal cross sectional view schematically showing aportion of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The arrangement of an embodiment of the present invention will now bedescribed with reference to the drawings. In FIG. 1, a pyroelectricdevice includes a main body casing composed of a can 4 and a stem 5 bothof which are formed of Kovar, the can 4 having a window hole 1 and afilter 2 composed of a silicon plate (or laminated interference filters)and fused and fixed to the window hole 1 by a fusing agent 3 of silversolder. A gold electrolytic plating is applied to the can 4 and the stem5 arranged as described above to form a surface treatment film 9. Threelead terminals, that is, a ground terminal 6, a source terminal 7 and adrain terminal 8 are attached to the stem 5 and connected to a mainelectric circuit of, for example, an unillustrated flame sensor or thelike. In this case, although the ground terminal 6 is directly and incontact with the stem 5, the other two terminals are fixed to the stem 5in a sealed state through insulating members 13 so as to be insulatedfrom the stem 5.

Since Kovar (Fe:Ni:Co=55:28:17) has a thermal expansion coefficientα=4.7×10⁻⁶ /°C. while silicon used for the filter 2 has a thermalexpansion coefficient α=2.4×10⁻⁶ /°C., the difference of the thermalexpansion coefficients is small. Therefore, when the can 4 is formed ofKovar, no mechanical trouble due to the difference of the thermalexpansion coefficients occurs at a junction portion. Since a steel plateused for a can in the prior art has a thermal expansion coefficientα=13.2×10⁻⁶ /°C., the employment of the Kovar is very useful as comparedwith the steel plate. Further, when sapphire is used for the filter 2,since the sapphire has a thermal expansion coefficient α=5.3×10⁻⁶ /°C.,a difference of the thermal expansion coefficients can be furtherreduced so that trouble due to the difference of the thermal expansioncoefficients can be likewise prevented in the same way.

Further, when the stem 5 is also composed of Kovar, since the can 4 andthe stem 5 have the same thermal expansion coefficient, trouble at thesealing portion 14 such as a mechanical strain or damage can be avoided.That is, the sealing portion 14 is entirely free from trouble due to thedifference of thermal expansion coefficients regardless of whether it isfused, adhesive-bonded or caulked. The sealing portion 14 of the presentembodiment is sealed and joined by electric spot welding making use ofresistance heating, and in this case a gold-plated treatment filmexisting there causes a disadvantage, and thus the treatment film 9 isnot provided with the sealing portion 14. When the treatment film 9 isnonelectrolytically plated with nickel, it need not be omitted from thesealing portion 14.

When the stem 5 is composed of Kovar as described above and the threeterminals 6, 7 and 8 are also composed of Kovar, these terminals can beadvantageously sealed by using glass as the insulating members 13. Inthis case, the three Kovar terminals 6, 7 and 8 are also subjected to asurface treatment. The can 4 is joined to the stem 5 at the sealingportion 14 to integrally form the casing. Although the gold plating isshown as the corrosion-resistant surface treatment film 9 in the aboveembodiment, a film coated with an organic polymer such as apolytetrafluoroethylene resin may be used.

A process for joining the filter 2 to the can 4 is such that the fusingagent 3 composed of silver solder is disposed about the circumference ofthe window hole 1 of the can 4 and the filter 2 is placed thereon. Then,the fusing agent 3 is heated to be melted under a reducing atmosphereexcluding oxygen and thereafter cooled. Thus, the fusing agent 3 iscaused to fit the circumference of the window hole 1 of the can 4 andthe outer periphery of the filter 2 so that the filter 2 can be fixed ina perfectly sealed state.

This joint made by the fusing is advantageous with regard to the sealingproperty and strength as compared with the joint made by a resinadhesive, and the penetration of the air from outside into the inside Aof the frame member can be completely shut off. The material used forthe fusing agent may be, for example, fusing glass in addition to thesilver solder.

When this process is executed in an atmosphere under a vacuum state, theinside A of the frame member can be placed in a vacuum state, and thusthe effects of humidity and the like in the remaining gas on the variousfunctional elements in the inside A of the frame member can beprevented. A conventional resin adhesive cannot keep the inside A of theframe member in the vacuum state because of the insufficient strengththereof. The vacuum state in the inside A of the frame member may beestablished by forming a pin hole through the stem 5, absorbing a gastherethrough, and thereafter sealing the pin hole. Further, theremaining gas may also be removed by replacing the gas in the inside Aof the frame member with an inert gas such as a nitrogen gas of highpurity.

Further, when the inside A of the frame member is placed in the vacuumstate, the performance of the device itself can be improved. Morespecifically, a pyroelectric member 11 as a member for detectinginfrared rays changes its electric characteristics as heat of theinfrared rays is absorbed and usually the absorbed infrared rays arepartially radiated in some forms. Thus, when the inside A of the framemember is kept in the vacuum state, no thermal convection is generatedin the inside and thus a thermal radiation due to a gas flow can beprevented. Therefore, a sensitivity and response speed of thepyroelectric device can be improved and at the same time an externalnoise can be reduced.

Various functional elements such as the pyroelectric member 11, acircuit element 33 such as an FET or the like are assembled in thecasing to carry out the function of a pyroelectric device. The terminalpins including the ground terminal 6, the source terminal 7 and thedrain terminal 8, which support the printed board 15 thereon and areconnected to wires for outputting an electric signal from thepyroelectric member 11, are provided with flat collars 17 disposed inthe extreme end regions of the respective pins on the inner side Of thecasing and arranged as the terminal pins with the collars (hereinafter,referred to as kneel pins). When the collar 17 is provided for each pin,an extreme end portion 18 projects from the collar 17. Each extreme endportion 18 is inserted into a pin hole 19 which is formed in the printedboard 15 and is fixed thereto by soldering or the like. At this time,the printed board 15 is fixed by being abutted against the uppersurfaces of the collars 17. The placement of the printed board 15 on thecollars 17 of the three terminal pins enables the pyroelectric member 11to be disposed in parallel with the plane of the filter and the like inthe casing together with the printed board 15. More specifically, anadvantage can be obtained in that a pyroelectric device with highaccuracy can be effectively manufactured by this arrangement.

The pyroelectric member 11 of the present invention will be described inmore detail with reference to FIGS. 2 and 3. The keyhole-shapedelectrodes 20 and 21 formed on the upper and lower surfaces of thepyroelectric member 11 include disc-shaped absorbing electrode portions22 and 23 disposed to confront each other across the pyroelectric member11, respectively, as well as projecting electrode portions 24 and 25projecting respectively in the opposite directions from the absorbingelectrode portions 22 and 23. The ends of the drawing electrode portions24 and 25 on the opposite sides of the absorbing electrodes areelectrically connected to unillustrated circuit patterns of the printedboard 15, which is located below the electrodes 20 and 21 through anelement base 32, by electrically conductive adhesives 26 and 27.

When the electrode 20 is manufactured, first, a keyhole-shaped thinlayer of a predetermined thickness is formed on one side of thepyroelectric member 11 by vapor deposition or the like. Thereafter, alayer is further laminated only on the portion projecting from thedisc-shaped portion of the keyhole shape, in the same way. Thus, theabsorbing electrode portion 22 having a layer of a predeterminedthickness is formed on the disc-shaped portion and the drawing electrode24 having a layer thicker than that of the absorbing electrode 22 isformed on the projecting portion. The electrode 21 is formed in the sameway as the electrode 20 so that the projecting portion of the drawingelectrode portion 25 projects in the direction opposite to that of thedrawing electrode portion 24. As a result, since the drawing electrodeportions 24 and 25 formed with a narrow width have a thicker layer, theelectric conductivity and durability of these electrode portions areimproved. The method of manufacturing the electrodes 20 and 21 is notlimited to the above mentioned method. Rather, a certain thickness of alayer may be previously formed on each of the drawing electrode portions24 and 25 and the absorbing electrode portions 22 and 23 may be formedthereon so that they have a predetermined thickness. Further, as anothermethod, the absorbing electrode portions and the drawing electrodeportions may be individually formed so that the former electrodeportions have a thicker layer than the latter electrode portions.

Another embodiment of the electrodes 20 and 21 will be described withreference to FIG. 4. Although the arrangement of these electrodes andthe method of making the same are substantially the same as those of theaforesaid electrodes, they differ in that the material of the absorbingelectrode portions is different from that of the drawing electrodeportions. More specifically, in the first layer formation executed byvapor deposition or the like, only the disc-shaped portions ofkeyhole-shapes are formed as the absorbing electrode portions 28 and 29by using an infrared ray absorbing material such as nickel chromiumalloy or the like. Then, when layers are laminated for drawing electrodeportions 30 and 31, a good conducting material such as platinum or othercorrosion resistive material is used to form projecting portions so thatthe end portions of the drawing electrode portions 30 and 31 areoverlaid with the absorbing electrode portions 28 and 29. With thisarrangement, the absorbing electrode portions 28 and 29 as thedisc-shaped portions of the electrodes 20 and 21 are composed of thenickel chromium alloy while the projecting portions of the drawingelectrode portions 30 and 31 are composed of platinum, and electricconductive adhesives 26 ad 27 are applied to the portion of theplatinum. As a result, the electrically conductivity and durability ofthe drawing electrode portions 30 and 31 are improved in the same way aswith the electrodes shown in FIGS. 2 and 3.

Further, as another method, in the first layer formation, akeyhole-shaped layer may be formed by using nickel chromium alloy andthereafter platinum may be laminated only on the projecting portion ofthe keyhole shape, as shown in FIG. 5. Thus, finally it suffices thatnickel chromium alloy is disposed on the light receiving surface of thepyroelectric member 11 and platinum is disposed on the surface, joinedto the electrically conductive adhesives 26 and 27.

The operation of the pyroelectric device will now be described. Thepyroelectric member 11 detects infrared rays passing through the filter2, converts the same to an electric signal, and outputs the electricsignal. The electric signal is applied to the gate of an unillustratedFET mounted on the printed board 15 to be amplified so that the signalis quantitatively detected as an amount of electricity proportional toan amount of the infrared rays. The pyroelectric member 11 may becomposed of PZT (lead zirconate titanate), tantalic acid lithium,titanate, PVDF (polyvinylidene fluoride), the copolymer thereof, or thelike.

As described above, since the surface of the can 4 and the stem 5constituting the casing is coated with the surface treatment film 9composed of the gold or nickel plated layer, the surface of thepyroelectric device does not become rusted and lose its weatherresistance even under severe environmental conditions such as highhumidity, and thus a practically applicable pyroelectric device can beobtained. Further, since the can 4 and the stem 5 constituting thecasing are composed of Kovar having a thermal expansion coefficientfairly near to that of the filter 2, strain, which results from thedifference of thermal expansion coefficients due to a thermal variation,is not caused at the junction between the can 4 and the stem 5 composedof the same material nor at the junction between the can 4 and thefilter 2 attached to the can 4. Therefore, no gap is generated at thejunction between the different materials and no crack is made in thefilter 2 even under severe environmental conditions. Thus, a practicallyapplicable device capable of maintaining an airtightness for a long timecan be obtained.

In addition to the above arrangement, the filter 2 is strongly fixed tothe window hole 1 of the can 4 in such a manner that the fusing agent 3such as silver solder or the like is placed along the circumference ofthe window hole 1, melted and then solidified. As a result, the windowhole 1 can be completely sealed so that corrosion of the pyroelectricmember 11 and the like caused by the penetration of the air from outsidecan be prevented. Further, since the joint strength of the respectiveportions is improved as described above, the inside A of the framemember can be placed under a reduced pressure (vacuum) state, by whichthe effect of remaining gas can be removed, if it remains within theframe member.

Further, since the terminal pins 6, 7 and 8 extending from the stem 5are arranged as the kneel pins each having the collar 17 radiallyprojecting at the extreme ends thereof on the inner side of the casing,the printed board 15 can be readily mounted in such a manner that theextreme ends 18 of the terminal pins axially extending from the collars17 are inserted into the pin holes 19 formed in the printed board 15 andthe lower surface of the printed board 15 is received by the collars 17.Thus, the pyroelectric member 11 mounted on the printed board and inparallel therewith can be disposed in parallel with the filter 2. Withthis arrangement, an effect can be obtained in that workability inproduction is improved and a pyroelectric device with high accuracy inconstruction and performance is provided.

Finally, since the absorbing electrode portions of the electrodes formedon the upper and lower surfaces of the pyroelectric member 11 have athickness or material different from those of the drawing electrodeportions, an effect can be obtained in that a corrosion resistivepyroelectric device excellent in durability is obtained.

I claim:
 1. A pyroelectric device comprising:a stem; a printed boardmounted on said stem; an element base mounted on said printed board; apyroelectric member mounted on said element base for detecting infraredrays; a can having a window hole formed therein and being fixed to saidstem in an airtight manner; a filter mounted to said can and sealinglycovering said window hole; an upper electrode formed on an upper surfaceof said pyroelectric member; a lower electrode formed on a lower surfaceof said pyroelectric member; wherein said printed board has an electriccircuit for outputting an electric signal corresponding to the infraredrays detected by said pyroelectric member; wherein each of said upperand lower electrodes includes an absorbing electrode portion composed ofan infrared ray absorbing material formed as a thin layer, and a drawingelectrode portion connected at a first end thereof with said absorbingelectrode portion and being formed as a layer thicker than said thinlayer of said absorbing electrode portion, a second end of said drawingelectrode portion of each of said upper and lower electrodes beingdisposed at an outer edge of said pyroelectric member; and whereinelectrically conductive adhesive portions are provided outside saidelement base between said printed board and a second end of said drawingelectrode portion of each of said upper and lower electrodes toelectrically connect said printed board with each of said upper andlower electrodes.
 2. A pyroelectric device comprising:a stem; a printedboard mounted on said stem; an element base mounted on said printedboard; a pyroelectric member mounted on said element base for detectinginfrared rays; a can having a window hole formed therein and being fixedto said stem in an airtight manner; a filter mounted to said can andsealingly covering said window hole; an upper electrode formed on anupper surface of said pyroelectric member; a lower electrode formed on alower surface of said pyroelectric member; wherein said printed boardhas an electric circuit for outputting an electric signal correspondingto the infrared rays detected by said pyroelectric member; wherein eachof said upper and lower electrodes includes an absorbing electrodeportion composed of an infrared ray absorbing material, and a drawingelectrode portion connected at a first end thereof with said absorbingelectrode portion and being composed of a corrosion resistive material,a second end of said drawing electrode portion of each of said upper andlower electrodes being disposed at an outer edge of said pyroelectricmember; and wherein electrically conductive adhesive portions areprovided outside said element base between said printed board and asecond end of said drawing electrode portion of each of said upper andlower electrodes to electrically connect said printed board with each ofsaid upper and lower electrodes.
 3. A pyroelectric device comprising:astem; a printed board mounted on said stem; a pyroelectric membermounted to said printed board for detecting infrared rays; a can havinga window hole formed therein and being fixed to said stem in an airtightmanner; an upper electrode formed on an upper surface of saidpyroelectric member; a lower electrode formed on a lower surface of saidpyroelectric member; a filter fixed to said can about a circumference ofsaid window hole by a solder for sealing said window hole; and whereinsaid printed board has an electric circuit for outputting an electricsignal corresponding to the infrared rays detected by said pyroelectricmember.
 4. A pyroelectric device as recited in claim 3, whereinsaidsolder is interposed between an upper surface of said filter and a lowersurface of a top wall of said can.